Such an apparatus is shown, for example, in U.S. Pat. No. 3,987,438. In the aforesaid patent, there is an array of plungers which are raised by energizing surrounding solenoids to project their upper ends from a display surface in imitation of braille and each plunger when raised is locked in its operative position by a ball which is moved under the plunger to prevent it from returning to its inoperative position. Each solenoid for lifting its associated plunger has an unlatching solenoid individual thereto, together with a plunger and spring. To unlatch a plunger, its associated unlatching solenoid has to be energized. This draws its plunger downwardly against the spring and the latching ball is drawn by the magnetic field into the unlocking position. Thus, for a row of 48 braille cells, 288 unlatching solenoids together with 280 plungers and 288 plunger springs are required for the unlatching process. In contrast with this, the present invention requires only a single unlatching plate for unlatching all of the 48 cells simultaneously. Thus, the structure and mode of operation for unlatching according to the present invention are very different and lead to an immense simplification over the prior art such as disclosed in the aforesaid patent.